Field of the Invention
The present invention relates to an image forming apparatus, such as a laser beam printer (LBP), a digital copier, or a multi-functional printer (multi-featured printer); and an optical scanning device included in the image forming apparatus.
Description of the Related Art
As the optical scanning device included in the image forming apparatus, there is known an optical scanning device that deflects light beams from a light source by a deflecting unit, and optically scans a scanned surface in a main-scanning direction. In such an optical scanning device, to optically scan the scanned surface with high accuracy, a synchronous detection unit is required for detecting the light beams deflected by the deflecting unit and determining a write-start position in the main-scanning direction on the scanned surface.
Japanese Patent Laid-Open No. 2009-115943 describes a configuration that separates light beams from a light source by a light-beam separating element, and guides the light beams respectively to a scanned surface and the synchronous detection unit. Also, Japanese Patent Laid-Open No. 2007-298997 describes a configuration that reflects light beams, which have passed through an end portion of an imaging lens, by using a mirror, and guides the light beams to a synchronous detection unit.
However, with the configurations of Japanese Patent Laid-Open No. 2009-115943 and Japanese Patent Laid-Open No. 2007-298997, since the light-beam separating element and mirror are required, the device may be complicated, and the synchronous detection with high accuracy may be no longer executed due to an arrangement error of respective components. Also, with the configurations of Japanese Patent Laid-Open No. 2009-115943 and Japanese Patent Laid-Open No. 2007-298997, respective members are required to be arranged so that light beams directed toward a scanned surface are not blocked in a main-scanning section, and hence the apparatus is not sufficiently reduced in size.